[turba] patch for readonly sources

[Chuck Hagenbuch]

Quoting Bo Daley <bo at tilda.com.au>:

> Actually the comments suggest that the 'export' attribute should be used
> to determine whether a source can be exported (eg. to CSV) rather than to
> determine whether or not to make it visible, so perhaps we need something
> like checkPermissions for sources too. Maybe something like this?

Not quite... we use the 'export' attribute to denote that a source has just
too many entries to export or to list all of - so the name isn't great, but
the use is relatively consistent.

-chuck

--
Charles Hagenbuch, <chuck at horde.org>
"... It is not more light we need, but more warmth! We die of cold, not of
darkness. It is not the night that kills, but the frost." - Miguel de
Unamuno